Novel illumination devices

ABSTRACT

Illumination device comprising at least one LED and at least one colour converter comprising at least one organic fluorescent colorant in a matrix consisting essentially of polystyrene or polycarbonate, wherein LED and colour converter are present in a remote phosphor arrangement.

The present invention has for its subject-matter illumination devicescomprising at least one LED and a colour converter comprising at leastone organic fluorescent colorant in a matrix consisting essentially ofpolystyrene or polycarbonate, wherein LED and colour converter arepresent in a remote phosphor arrangement.

The invention further provides colour converters comprising at least oneorganic fluorescent colorant in a matrix consisting essentially ofpolystyrene or polycarbonate.

20% of global electrical energy consumption is required for lightingpurposes. Lighting equipment is the subject of further technicaldevelopment with regard to the energy efficiency, colour reproduction,service life, manufacturing costs and usability thereof. Incandescentlamps and halogen lamps, being thermal radiators, produce light withvery good colour reproduction since a broad spectrum is emitted withradiation characteristics approaching Planck's law of black bodyradiation and closely resembling sunlight. One disadvantage ofincandescent lamps is the high power consumption thereof, since a verylarge amount of electrical energy is converted to heat.

A higher efficiency is possessed by compact fluorescent tubes, whichproduce a linear emission spectrum of mercury by discharge of anelectrically excited mercury vapour. On the inside of these compactfluorescent tubes are phosphors comprising rare earths, which absorbsome of the mercury emission spectrum arid emit it as green and redlight. The emission spectrum of a compact fluorescent tube is composedof different lines, which results in much poorer colour reproduction.The light of a compact fluorescent tube is perceived by many humans tobe less natural and less pleasant than sunlight or light fromincandescent lamps.

A longer lifetime and a very good energy efficiency are exhibited bymost light-emitting diodes (LEDs). The light emission is based on therecombination of electron-hole pairs (excitor's) in the junction area ofa forward-biased semiconductor pn junction. The size of the band gap ofthis semiconductor determines the approximate wavelength. LEDs can beproduced in different colours.

Stable and energy-efficient blue LEDs can produce white light by colourconversion. According to a known method for this purpose, a polymericmaterial comprising a radiation conversion phosphor is applied directlyto the LED light source (LED chip). Frequently, the polymeric materialis applied to the LED chip in approximately droplet or hemisphericalform, as a result of which particular optical effects contribute to theemission of light. Such structures in which radiation conversionphosphor in a polymeric matrix is applied directly and withoutintervening space to an LED chip are also referred to as “phosphor on achip”. In phosphor on a chip LEDs, the radiation conversion phosphorsused are generally inorganic materials. The radiation conversionphosphors, which may consist, for example, of cerium-doped yttriumaluminium garnet, absorb a certain proportion of the blue light and emitlonger-wave light with a broad emission band, such that the mixing ofthe transmitted blue light and of the emitted light gives rise to whitelight.

In order to improve the colour reproduction of such lighting elements,it is additionally possible to incorporate a red-emitting diode as wellas the white light diode described. This makes it possible to producelight which is perceived to be more pleasant by many people. However,this is more inconvenient and costly in technical terms.

In phosphor on a chip LEDs, the polymeric material and the radiationconversion phosphor are subject to relatively high thermal and radiativestress. For this reason, organic radiation conversion phosphors have notbeen suitable to date for use in phosphor on a chip LEDs. Organicfluorescent colorants can in principle produce good colour reproductionby virtue of their broad emission bands. However, they are to date notstable enough to withstand the thermal and radiative stresses in thecase of direct arrangement on the LED chip.

In order to produce white light from blue light by colour conversion,there is a further concept in which the colour converter (also referredto simply as “converter”), which generally comprises a carrier and apolymeric coating, is a certain distance away from the LED chip. Such astructure is referred to as “remote phosphor”.

The spatial distance between the primary light source, the LED, and thecolour converter reduces the stress resulting from heat and radiation tosuch an extent that the requirements on the stability can be achieved bysuitable organic fluorescent dyes. Furthermore, LEDs according to the“remote phosphor” concept are even more energy-efficient than thoseaccording to the “phosphor on a chip” concept. The use of organicfluorescent dyes in these converters offers various advantages. Firstly,organic fluorescent dyes give a much higher yield due to theirsubstantially higher mass-specific absorption, which means thatconsiderably less material is required for efficient radiationconversion than in the case of inorganic radiation converters. Secondly,they enable good colour reproduction and are capable of producingpleasant light. Furthermore, they do not require any materialscomprising rare earths, which have to be mined and provided in a costlyand inconvenient manner and are only available to a limited degree. Itis therefore desirable to provide colour converters for LEDs whichcomprise suitable organic fluorescent dyes and have a long lifetime.

DE 10 2008 057 720 A1 describes the concept of remote phosphor LEDs anddiscloses, in addition to a conversion layer comprising inorganicradiation conversion phosphors, the use of organic radiation conversionphosphors embedded into a polymeric matrix. The polymeric matricesmentioned are, for example, silicones, epoxides, acrylates orpolycarbonates.

WO 03/038915 A describes the use of perylene dyes as a radiationconversion phosphor for phosphor on a chip LEDs. In LEDs according tothis document, the organic dyes are embedded into a matrix composed of abisphenol A-based epoxy resin.

US 20080252198 discloses colour converters comprising a combination ofred fluorescent dyes based on perylene derivatives with furtherfluorescent dyes. These are embedded into a transparent medium, whichmay be, for example, polyvinylpyrrolidone, polymethacrylate,polystyrene, polycarbonate, polyvinyl acetate, polyvinyl chloride,polybutene, polyethylene glycol, an epoxy resin.

It was an object of the present invention to provide illuminationdevices and colour converters based on organic fluorescent dyes, whichdo not have the disadvantages of the prior art and which especially havea long lifetime. In addition, they should have a high fluorescencequantum yield.

The object was achieved by the illuminati n devices and colourconverters cited at the outset.

Inventive illumination devices comprise at least one LED and at leastone colour converter. Colour converters likewise form pert of thesubject-matter of the present invention and comprise, in accordance withthe invention, at least one organic fluorescent colorant in a matrixconsisting essentially of polystyrene and/or polycarbonate.

In the context of this invention, colour converters are understood tomean devices which are capable of absorbing light of particularwavelengths arid converting it to light of other wavelengths.

The LEDs of technical relevance are frequently blue LEDs which emitlight with a peak wavelength of, for example, 420 to 480 nm, preferably440 to 470 nm, most preferably at 445 to 460 nm.

According to the selection of the radiation conversion phosphors and ofthe wavelength absorbed, it is possible that inventive colour convertersemit light in a wide variety of colours. In many cases, however, the aimis to obtain white light.

Radiation conversion phosphors include all materials which are capableof absorbing light of a particular wavelength and converting it to lightof another wavelength. Such materials are also referred to as phosphorsor fluorescent colorants.

Radiation conversion phosphors may, for example, be inorganicfluorescent colorants such as cerium-doped yttrium aluminium garnet, ororganic fluorescent colorants. Organic fluorescent colorants may beorganic fluorescent pigments or organic fluorescent dyes.

Inventive colour converters comprise at least one organic fluorescentcolorant present embedded in a polymeric matrix consisting essentiallyof polycarbonate or polystyrene. Suitable organic fluorescent colorantsare in principle all organic dyes or pigments which can absorb light ofa particular wavelength and convert it to light of another wavelength,which can be dissolved or distributed homogeneously in a polymericmatrix, and which have sufficient stability to thermal and radiativestress.

Preferred organic pigments are, for example, perylene pigments.

Typically, suitable organic pigments have a mean particle size to DIN13320 of 0.01 to 10 μm, preferably 0.1 to 1 μm.

Suitable organic fluorescent dyes fluoresce in the visible range of thespectrum and are, for example, the green-, orange- or red-fluorescingfluorescent dyes listed in the Colour Index.

Preferred organic fluorescent dyes are functionalized naphthalene orrylene derivatives.

Preferred naphthalene derivatives are green-, orange- or red-fluorescingfluorescent dyes comprising a naphthalene unit.

Preference is further given to naphthalene derivatives which bear one ormore substituents selected from halogen, cyano, benzimidazole, or one ormore radicals bearing carbonyl functions. Suitable carbonyl functionsare, for example, carboxylic esters, dicarboximides, carboxylic acids,carboxamides.

Preferred rylene derivatives comprise a perylene unit. A preferredembodiment relates to green-, orange- or red-fluorescing perylenes.

Preference is given to perylene derivatives which bear one or moresubstituents selected from halogen, cyano, benzimidazole, or one or moreradicals bearing carbonyl functions. Suitable carbonyl functions are,for example, carboxylic esters, carboximides, carboxylic acids,carboxamides.

Preferred perylene derivatives are, for example, the perylenederivatives specified in WO2007/006717 oh page 1, line 5 to page 22,line 6.

In a particularly preferred embodiment, suitable organic fluorescentdyes are perylene derivatives selected from Formulae II to VI

where R¹ is a linear or branched C₁-C₁₈ alkyl radical, C₄-C₈ cycloalkylradical which may be mono- or polysubstituted by halogen or by linear orbranched C₁-C₁₈ alkyl, or phenyl or naphthyl, where phenyl and naphthylmay be mono- or polysubstituted by halogen or by linear or branchedC₁-C₁₈ alkyl.

In one embodiment, R¹ in Formulae II to VI represents compounds withwhat is called swallowtail substitution, as specified in WO 2009/037283A1 at page 16 line 19 to page 25 line 8. In a preferred embodiment. R¹is a 1-alkylalkyl, for example 1-ethylpropyl, 1-propylbutyl,1-butylpentyl, 1-pentylhexyl or 1-hexylheptyl.

In Formulae II to VI, X represents substituents in the ortho and/or paraposition. X is preferably linear or branched C₁ to C₁₈ alkyl.

“y” indicates the number of substituents X. “y” is a number from 0 to 3.

More preferably, R¹ in Formulae II to VI is 2,4-di(tert-butyl)phenyl or2,6-disubstituted phenyl, especially preferably 2,6-diphenylphenyl,2,6-diisopropylphenyl.

Especially preferably, X is tert-butyl in the ortho/para position and/orsecondary alkyl, especially isopropyl, in the ortho positions or phenylin the ortho positions.

According to a specific aspect of this embodiment, the organicfluorescent dyes are selected fromN,N′-bis(2,6-diisopropylphenyl)-1,6-di(2,6-diisopropylphenoxy)-perylene-3,4:9,10-tetracarboximide,N,N′-bis(2,6-diisopropylphenyl)-1,7-di(2,6-diisopropylphenoxyyperylene-3,4:9,10-tetracarboximideand mixtures thereof.

According to a further specific aspect of this embodiment, the organicfluorescent dye is N-(2,6-di(isopropyl)phenyl)perylene-3,4-dicarboxylicmonoimide.

A further preferred fluoresecent dye is a dye of the Formula VI, e.g.N,N′-bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxdiimide(Lumogen® Red 300).

In a further particularly preferred embodiment, suitable organicfluorescent dyes are perylene derivatives selected from Formulae VII toX,

where R¹ in Formulae VII to X is a linear or branched C₁-C₁₈ alkylradical, a C₄-C₈ cycloalkyl radical which may be mono- orpolysubstituted by halogen or by linear or branched C₁-C₁₈ alkyl, orphenyl or naphthyl, where phenyl and naphthyl may be mono- orpolysubstituted by halogen or by linear or branched C₁-C₁₈ alkyl.

In one embodiment, R¹ in Formulae VII to X represents compounds withwhat is called swallowtail substitution, as specified in WO 2009/037283A1 at page 16 line 19 to page 25 line 8. In a preferred embodiment. R¹is a 1-alkylalkyl, for example 1-ethylpropyl, 1-propylbutyl,1-butylpentyl, 1-pentylhexyl or 1-hexylheptyl.

Especially preferably, R¹ in Formulae VII to X is linear or branched C₁to C₆ alkyl, especially n-butyl, sec-butyl, 2-ethylhexyl. Especiallypreferably, R¹ in Formulae VII to X is also isobutyl.

According to a specific aspect of this embodiment, the organicfluorescent dyes are selected from3,9-dicyanoperylene-4,10-bis(sec-butyl carboxylate),3,10-dicyanoperylene-4,9-bis(sec-butyl carboxylate) and mixturesthereof.

According to a further specific aspect of this embodiment, the organicfluorescent dyes are selected from 3,9-dicyanoperylene-4,10-bis(isobutylcarboxylate), 3,10-dicyanoperylene-4,9-bis(isobutyl carboxylate) andmixtures thereof.

Further preferred fluorescent dyes are Disperse Yellow 199, SolventYellow 98, Disperse Yellow 13, Disperse Yellow 11, Disperse Yellow 239,Solvent Yellow 159

In a preferred embodiment, the at least one organic fluorescent colorantis selected fromN,N′-bis(2,6-diisopropylphenyl)-1,7-di(2,6-diisopropylphenoxy)perylene-3,4:9,10-tetracarboxdiimide,N,N′-bis(2,6-diisopropylphenyl)-1,6-di(2,6-diisopropylphenoxy)perylene-3,4:9,10-tetracarboxdiimide,3,9-dicyanoperylene-4,10-bis(sec-butyl carboxylate),3,10-dicyanoperylene-4,9-bis(sec-butyl carboxylate),3,9-dicyanoperylene-4,10-bis(isobutyl carboxylate),3,10-dicyanoperylene-4,9-bis(isobutyl carboxylate),N-(2,6-di(isopropyl)phenyl)perylene-3,4-dicarboxylic monoimide andmixtures thereof.

In a preferred embodiment, colour converters comprise at least twodifferent organic fluorescent dyes. For example, a green-fluorescingfluorescent dye can be combined with a red-fluorescing fluorescent dye.Green-fluorescing fluorescent dyes are understood to mean especiallythose yellow dyes which absorb blue light and emit green or yellow-greenfluorescent light. Suitable red dyes absorb either the blue light of theLED directly or absorb the green light emitted by other dyes present,and transmit red fluorescent light.

In a less preferred embodiment, inventive colour converters compriseonly a single organic fluorescent dye, for example an orange fluorescentdye.

According to the invention, organic fluorescent dyes are embedded into amatrix consisting essentially of polystyrene and/or polycarbonate.

When the organic fluorescent colorants are pigments, these are generallypresent dispersed in the matrix.

Organic fluorescent dyes may be present either dissolved in the matrixor as a homogeneously distributed mixture. The organic fluorescent dyesare preferably present dissolved in the matrix.

Suitable matrix materials are organic polymers consisting essentially ofpolystyrene and/or polycarbonate.

In a preferred embodiment, the matrix consists of polystyrene orpolycarbonate.

Polystyrene is understood here to include all homo- or copolymers whichresult from polymerization of styrene and/or derivatives of styrene.

Derivatives of styrene are, for example, alkylstyrenes such asalpha-methylstyrene, ortho-, meta-, para-methylstyrene,para-butylstyrene, especially para-tert-butylstyrene, alkoxystyrene suchas para-methoxystyrene, para-butoxystyrene, para-tert-butoxystyrene.

In general, suitable polystyrenes have mean molar mass M_(n) of 10 000to 1 000 000 g/mol (determined by GPC), preferably 20 000 to 750 000g/mol, more preferably 30 000 to 500 000 g/mol.

In a preferred embodiment, the matrix of the colour converter consistsessentially or completely of a hompolymer of styrene or styrenederivatives.

In further preferred embodiments of the invention, the matrix consistsessentially or completely of a styrene copolymer which, in the contextof this application, are likewise considered to be polystyrene. Styrenecopolymers may comprise, as further constituents, for example,butadiene, acrylonitrile, maleic anhydride, vinylcarbazole or esters ofacrylic acid, methacrylic acid or itaconic acid as monomers. Suitablestyrene copolymers comprise generally at least 20% by weight of styrene,preferably at least 40% by weight and more preferably at least 60% byweight of styrene. In another embodiment, they comprise at least 90% byweight of styrene. Preferred styrene copolymers arestyrene-acrylonitrile copolymers (SAN) andacrylonitrile-butadiene-styrene copolymers (ABS),styrene-1,1′-diphenylethene copolymers, acrylicester-styrene-acrylonitrile copolymers (ASA), methylmethacrylate-acrylonitrile-butadiene-styrene copolymers (MABS).

A further preferred polymer is alpha-methylstyrene-acrylonitrilecopolymer (AMSAN).

The styrene homo- or copolymers can be prepared, for example, byfree-radical polymerization, cationic polymerization, anionicpolymerization, or under the influence of organometallic catalysts (forexample Ziegler-Natta catalysis). This can lead to isotactic,syndiotactic, atactic polystyrene or copolymers. They are preferablyprepared by free-radical polymerization. The polymerization can beperformed as a suspension polymerization, emulsion polymerization,solution polymerization or bulk polymerization.

The preparation of suitable polystyrenes is described, for example, inOscar Nuyken, Polystyrenes and Other Aromatic Polyvinyl Compounds, inKricheldorf, Nuyken, Swift, New York 2005, p. 73-150 and referencescited therein; and in Elias, Macromolecules, Weinheim 2007, p. 269-275.

Polycarbonates are polyesters of carbonic acid with aromatic oraliphatic dihydroxyl compounds. Preferred dihydroxyl compounds are, forexample, methylenediphenylenedihydroxyl compounds, for example bisphenolA.

One means of preparing polycarbonates is the reaction of suitabledihydroxyl compounds with phosgene in an interfacial polymerization.Another means is the reaction with diesters of carbonic acid, such asdiphenyl carbonate, in a condensation polymerization.

The preparation of suitable polycarbonates is described, for example, inElias, Macromolecules, Weinheim 2007, p. 343-347.

In a preferred embodiment, polystyrenes or polycarbonates which havebeen polymerized with the exclusion of oxygen are used. The monomerspreferably comprised, during the polymerization, a total of at most 1000ppm of oxygen, more preferably at most 100 ppm and especially preferablyat most 10 ppm.

Suitable polystyrenes or polycarbonates may comprise, as furtherconstituents, additives such as flame retardants, antioxidants, lightstabilizers, free-radical scavengers, antistats. Such stabilizers areknown to those skilled in the art.

In a preferred embodiment of the invention, suitable polystyrenes orpolycarbonates do not comprise any antioxidants or free-radicalscavengers.

In one embodiment of the invention, suitable polystyrenes orpolycarbonates are transparent polymers.

In another embodiment, suitable polystyrenes polycarbonates are opaquepolymers.

In one embodiment of the invention, the matrix consists essentially orcompletely of a mixture of polystyrene and/or polycarbonate with otherpolymers, but the matrix preferably comprises at least 25% by weight,more preferably 50% by weight, most preferably at least 70% by weight,of polystyrene and/or polycarbonate.

In another embodiment, the matrix consists essentially or completely ofa mixture of polystyrene or polycarbonate in any ratio.

In another embodiment, the matrix consists of mixtures of differentpolystyrenes and polycarbonates.

In one embodiment, the matrix is mechanically reinforced with glassfibres.

It has been found that, surprisingly, the stability of the organicfluorescent colorant is increased in polystyrene or polycarbonatecompared to other matrix materials.

For the execution of the invention, the geometric arrangement in whichthe organic fluorescent colorant-comprising matrix is present is notcrucial. The organic fluorescent colorant-comprising matrix may bepresent, for example, in the form of films, sheets or plaques. Theorganic fluorescent colorant-comprising matrix may likewise be indroplet or hemispherical form, or in the form of lenses with convexand/or concave, flat or spherical surfaces.

Irrespective of the three-dimensional shape, inventive converters may,for example, consist of a single layer or have a multilayer structure.

When inventive colour converters comprise more than one fluorescentcolorant, it is possible in one embodiment of the invention for severalfluorescent colorants to be present alongside one another in one layer.

In another embodiment, the different fluorescent colorants are presentin different layers.

In one embodiment of the invention, the organic fluorescentdye-comprising polymer layers (matrices) are 25 to 200 micrometres inthickness, preferably 35 to 150 μm and particularly 50 to 100 μm.

In another embodiment, the organic fluorescent dye-comprising polymerlayers are 0.2 to 5 millimetres in thickness, preferably 0.3 to 3 mm,more preferably 0.4 to 1 mn.

When the colour converters consist of one layer or have a layerstructure, the individual layers in a preferred embodiment arecontinuous and do not have any holes or interruptions, such that lightemitted by the LED must in each case pass through at least one organicfluorescent colorant-comprising matrix.

The concentration of the organic fluorescent colorants in the matrixdepends on factors including the thickness of the polymer layer. If athin polymer layer is used, the concentration of the organic fluorescentcolorant is generally higher than in the case of a thick polymer layer.The concentration of the organic fluorescent dyes is typically 0.001 to0.5% by weight, preferably 0.002 to 0.1% by weight, most preferably0.005 to 0.05% by weight, based in each case on the amount of the matrixmaterial.

Organic pigments are generally used in a concentration of 0.001 to 0.5%by weight, preferably 0.005 to 0.2% by weight, more preferably 0.01 to0.1% by weight, based in each case on the amount of the matrix material.

In a preferred embodiment, at least one of he layers or matricescomprising organic fluorescent dye comprises scattering bodies forlight.

In a further preferred embodiment of the multilayer structure, severallayers comprising fluorescent dye and one or more layers comprisingscatterers without fluorescent dye are present.

Suitable scattering bodies are inorganic white pigments, for exampletitanium dioxide, barium sulphate, lithopone, zinc oxide, zinc sulphide,calcium carbonate with a mean particle size to DIN 13320 of 0.01 to 10μm, preferably 0.1 to 1 μm, more preferably 0.15 to 0.4 μm.

Scattering bodies are included typically in an amount of 0.01 to 2.0% byweight, preferably 0.05 to 0.5% by weight, more preferably 0.1 to 0.4%by weight, based in each case on the polymer of the layer comprisingscattering bodies.

Inventive colour converters may optionally comprise furtherconstituents, such as a carrier layer. Carrier layers serve to impartmechanical stability to the colour converter. The type of material ofthe carrier layers is not crucial, provided that it is transparent andhas the desired mechanical strength. Suitable materials for carrierlayers are, for example, glass or transparent rigid organic polymers,such as polycarbonate, polystyrene or polymethacrylates or polymethylmethacrylates.

Carrier layers generally have a thickness of 0.1 mm to 10 mm, preferably0.3 mm to 5 mm, more preferably 0.5 mm to 2 mm.

Inventive colour converters are suitable or the conversion of lightproduced by LEDs.

Inventive colour converters can be used in combination with LEDs invirtually any geometric form and independently of the structure of theillumination device.

Preference is given to using inventive colour converters in a remotephosphor structure. The colour converter here is spatially separatedfrom the LED. In general, the distance between LED and colour converteris from 0.1 cm to 50 cm, preferably 0.2 to 10 cm and most preferably 0.5to 2 cm. Different media such as air, noble gases, nitrogen or othergases or mixtures thereof may be present between colour converter andLED.

The colour converter may, for example, be arranged concentrically aroundtie LED, or in the form of a flat layer, plaque or sheet.

Inventive colour converters and illumination devices exhibit, onirradiation with LED light, compared to those known from the prior art,a long lifetime and a high quantum yield, and emit pleasant light withgood colour reproduction.

Inventive illumination devices are suitable for illumination indoors,outdoors, illumination of offices and of vehicles, and in torches, gamesconsoles, street lights, illuminated traffic signs.

The invention further provides a process for producing colour converterscomprising at least one organic colorant.

In one embodiment of the invention, a process for producing colourconverters comprising an organic fluorescent dye comprises theproduction of a polymer film, wherein the organic fluorescent dyes aredissolved or dispersed in an organic solvent together with the matrixmaterial and optionally scattering particles, and processed to a polymerfilm with homogeneously distributed dye by removing the solvent.

Other embodiments of the invention comprise the extrusion and/orinjection-moulding of polystyrene or polycarbonate with organicfluorescent colorants.

EXAMPLES

Materials Used:

Polymer 1: transparent homopolymer of methyl methacrylate with a Vicatsoftening temperature of 96° C. to DIN EN ISO 306, (Plexiglas® 6N fromEvonik)

Polymer 2: transparent polycarbonate based on a polycondensate ofbisphenol A and phosgene (Makrolon® 3119 from Bayer)

Polymer 3: transparent polystyrene based on a homopolymer of styrenewith a density of 1048 kg/m3 and a Vicat softening temperature of 98° C.to DIN EN ISO 306 (PS 168 N from BASF SE)

Dye 1: Yellow/green-fluorescing fluorescent dye consisting of a mixtureof 3,9-dicyanoperylene-4,10-bis(Sec-butyl carboxylate) and3,10-dicyanoperylene-4,9-bis(sec-butyl carboxylate).

Dye 2: Yellow/green-fluorescing fluorescent dye namedN-(2,6-di(isopropyl)phenyl)perylene-3,4-dicarboxylic monoimide.

Titanium dioxide: TiO₂ rutile pigment from the sulphate process with amean scattering power to DIN 53165 of 94.0 to 100 (Kronos® 2056 fromKronos Titan)

Production of the Colour Converters:

Approx. 2.5 g of polymer and 0.03% or 0.05% by weight of dye (based onthe mass of the polymer) were dissolved in approx. 5 ml of methylenechloride, and 0.1% or 0.5% by weight of TiO₂ was dispersed therein.

The resulting solution/dispersion was coated onto a glass surface with abox-type coating bar (wet film thickness 400 μm). After the solvent haddried off, the film was detached from the glass and dried at 50° C. in avacuum drying cabinet overnight.

Circular film pieces with a diameter of 15 mm were punched out of thisfilm, and then served as test samples.

The following samples were produced and analyzed:

TiO₂ Film No. Polymer Dye Dye content* content* thickness 1 1 1 0.05% byweight 0.1% by weight 57 μm 2 2 1 0.03% by weight 0.5% by weight 68 μm 33 1 0.03% by weight 0.1% by weight 73 μm 4 1 2 0.05% by weight 0.1% byweight 43 μm 5 2 2 0.03% by weight 0.5% by weight 69 μm 6 3 2 0.03% byweight 0.1% by weight 73 μm *based on the amount of polymer used

Exposure of the Samples:

The samples were exposed with an exposure apparatus composed ofcommercially available GaN-LEDs of the Luxeon V-Star series (fromLumileds Lighting), LXHL-LR5C royal blue model, which were constructedtogether with reflector optics on a cooling unit. The LEDs were operatedat approx. 550-700 mA, with all exposure stations set to the sameintensity. The irradiation was effected with light of wavelength 455 nm.The luminance was approx. 0.09 W/cm².

Determination of the Lifetime of the Samples

For analysis, the samples were removed from the exposure stations andanalyzed in the C9920-02 quantum yield measuring system (fromHamamatsu). This involved illuminating each of the samples in anintegrating sphere (Ulbricht sphere) with light of 450-455 nm. Bycomparison with the reference measurement in the Ulbricht sphere withouta sample, the unabsorbed fraction of the excitation light and thefluorescence light emitted by the sample are determined by means of aCCD spectrometer. Integration of the intensities over the unabsorbedexcitation light or over the emitted fluorescence light gives the degreeof absorption or fluorescence intensity or fluorescence quantum yield ofeach sample.

Each of the specimens was exposed constantly over a period of 20 daysand removed from the exposure apparatus only to determine the degree ofabsorption, the fluorescence intensity and the fluorescence quantumyield of the colour converters.

FIGS. 1 and 3 show, on the abscissa, the exposure time in days and, onthe ordinate, the percentage of the incident light (450-455 nm) whichhas been absorbed.

The numbers beside the three curves corresponds to the sample numbers.

It was found in all cases that the absorption of the light by thesamples decreased with exposure time, but that the decrease in the caseof inventive colour converters composed of polystyrene or polycarbonate(samples 2, 3, 5 and 6) was much slower than in the case of noninventivecolour converters (samples 1 and 4).

FIGS. 2 and 4 show, on the abscissa, the exposure time in days and, onthe ordinate, the relative fluorescence intensity.

The numbers beside the three curves correspond to the sample numbers.

It was found in all cases that the fluorescence intensity of samplesdecrease with time, but that the decrease was much slower in the case ofinventive colour converters of polystyrene or polycarbonate (samples 2,3, 5 and 6) than in the case of noninventive colour converters (samples1 and 4).

1: An illumination device, comprising at least one LED and at least onecolour converter comprising at least one organic fluorescent colorant ina matrix consisting essentially of polystyrene or polycarbonate, whereinthe LED and the colour converter are present in a remote phosphorarrangement. 2: The illumination device of claim 1, wherein the at leastone organic fluorescent colorant is an organic fluorescent dye. 3: Theillumination device of claim 1, Illumination wherein the at least oneorganic fluorescent colorant is a green- or red- or orange-fluorescingorganic fluorescent dye. 4: The illumination device of claim 1, whereinthe at least one organic fluorescent colorant is a naphthalene orperylene derivative. 5: The illumination device of claim 1, wherein theat least one organic fluorescent colorant is selected from the groupconsisting of

wherein: R¹ is a linear or branched C₁-C₁₈ alkyl radical, a C₄-C₈cycloalkyl radical which may be mono- or polysubstituted by halogen orby linear or branched C₁-C₁₈ alkyl, or phenyl or naphthyl, where phenyland naphthyl may be mono- or polysubstituted by halogen or by linear orbranched C₁-C₁₈ alkyl; X represents substituents in the ortho and/orpara position and is linear or branched C₁ to C₁₈ alkyl; and is a numberfrom 0 to
 3. 6: The illumination device of claim 5, wherein the at leastone organic fluorescent colorant is selected from the group consistingofN,N′-bis(2,6-diisopropylphenyl)-1,7-di(2,6-diisopropyl-phenoxy)perylene-3,4:9,10-tetracarboxdiimide,N,N′-bis(2,6-diisopropylphenyl)-1,6-di(2,6-diisopropylphexy)perylene-3,4:9,10-tetracarboxdiimide,3,9-dicyanoperylene-4,10-bis(sec-butyl carboxylate),3,10-dicyanoperylene-4,9-bis(sec-butyl carboxylate),3,9-dicyanoperylene-4,10-bis(isobutyl carboxylate),3,10-dicyanoperylene-4,9-bis(isobutyl carboxylate),N-(2,6-di(isopropyl)phenyl)perylene-3,4-dicarboxylic monomide andmixtures thereof. 7: The illumination device according to claim 6,wherein the at least one organic fluorescent colorant is selected fromthe group consisting ofN,N′-bis(2,6-diisopropylphenyl)-1,7-di(2,6-diisopropylphenoxy)perylene-3,4:9,10-tetracarboxdiimide,N,N′-bis(2,6-diisopropylphenyl)-1,6-di(2,6-diisopropylphenoxy)perylene-3,4:9,10-tetracarboxdiimideand mixtures thereof. 8: A color converter, comprising at least oneorganic fluorescent dye in a matrix consisting essentially ofpolystyrene or polycarbonate, wherein the at least one organicfluorescent dye is selected from the group consisting of

wherein: R¹ is a linear or branched C₁-C₁₈ alkyl radical, a C₄-C₈cycloalkyl radical which may be mono- or polysubstituted by halogen orby linear or branched C₁-C₁₈ alkyl, or phenyl or naphthyl, where phenyland naphthyl may be mono- or polysubstituted by halogen or by linear orbranched C₁-C₁₈ alkyl; X represents substituents in the ortho and/orpara position and is linear or branched C₁ to C₁₈ alkyl; and y is anumber from 0 to
 3. 9: The color converter according to claim 8, whereinthe at least one organic fluorescent dye is selected from the groupconsisting ofN,N′-bis(2,6-diisopropylphenyl)-1,7-di(2,6-diisopropylphenoxy)perylene-3,4:9,10-tetracarboxdiimide,N,N′-bis(2,6-diisopropylphenyl)-1,6-di(2,6-diisopropyl-phenoxy)perylene-3,4:9,10-tetracarboxdiimide,3,9-dicyanoperylene-4,10-bis(sec-butyl carboxylate),3,10-dicyanoperylene-4,9-bis(sec-butyl carboxylate),3,9-dicyanoperylene-4,10-bis isobutyl carboxylate),3,10-dicyanoperylene-4,9-bis(isobutyl carboxylate),N-(2,6)-di(isopropyl)phenyl)perylene-3,4-dicarboxylic monoimide andmixtures thereof. 10: The color converter according to claim 9, whereinthe at least one organic fluorescent dye is selected from the groupconsisting ofN,N′-bis(2,6-diisopropylphenyl)-1,7-di(2,6-diisopropylphenoxy)perylene-3,4:9,10-tetracarboxdiimide,N,N′-bis(2,6-diisopropylphenyl)-1,6-di(2,6-diisopropyl-phenoxy)perylene-3,4:9,10-tetracarboxdiimideand mixture thereof. 11: The color converter according to claim 8,wherein the at least one organic fluorescent colorant is dissolved inthe matrix. 12: The color converter of claim 8, further comprising atleast one inorganic white pigment as a scattering body. 13: The colorconverter of claim 8, which is a film, a plaque or a sheet. 14: Aprocess for producing the color converter of claim 8, the processcomprising dissolving the at least one organic fluorescent colorant inan organic solvent together with the matrix material and optionallyscattering particles, and processing a resulting mixture into a film byremoving the solvent. 15: The process of claim 14, further comprisingextruding and/or injection-molding the matrix with the at least oneorganic fluorescent colorant. 16: A process, comprising converting lightproduced by LEDs with at least one color converter according to claim 8.17: A remote phosphor structure, comprising the color converter of claim8 and at least one LED.